In general, Ethernet is a point-to-point communication technology. More complex networks are created by using layer 2 (according to the ISO/OSI stack) bridges (also called switches). Switches enable the definition of complex network topologies and offer many services including the basic relaying of frames (the basic Ethernet communication element) from one source node to multiple destinations, and more complex operations such as channel bandwidth allocation, network partitioning via virtual LANs (VLANs) and traffic prioritization.
The bandwidth requirements of modern and future automotive applications are posing a relevant challenge to current in-vehicle networking (IVN) technologies such as Controller Area Network (CAN) and FlexRay. Thanks to the latest development of the Ethernet technology, a 100 Mbps Ethernet link can now be implemented and a 1 Gbps link will be available in near future. Switched Ethernet networks are of particular interest in the automotive market for supporting bandwidth-intensive applications such as backbones interconnecting various domains, infotainment and surround-view applications. Usually, Ethernet implementation in the automotive field but not limited thereto the use of unshielded twisted pair of copper wires is preferred because of weight and cost reasons. However, unshielded twisted pair cabling poses problems in meeting EMC (electromagnetic compatibility) requirements, e.g. imposed by regulatory standards.
Since more and more complex electromagnetic environment in an electronic system, electromagnetic interference (EMI) phenomenon is much worse and becomes an obvious obstacle affecting regular operation of the system. Since rapid development of high speed digital circuits, researchers are driven to pay attention to suppress noise and crosstalk of digital system. Ideally, a differential signal may maintain well original signal aspect and maintain low electromagnetic radiation or electromagnetic interference. However, in an actual circuit, unbalanced delay and amplitude, or unbalanced design of input/output register or package layout may cause the differential signal to generate different rising/falling edge time such that unwanted common mode noise attaches the differential signal. With respect to high speed data transmission interface, for instance, Gigabit Ethernet, etc., a cable is always needed to transmit the differential signals between different electronic devices. At this time, a common mode noise may be coupled to an input/output cable and is formed to be an excitation source such that the input/output cable becomes an EMI antenna.
Hence, in order to solve electromagnetic interference (EMI) problem of the input/output cable, it is advantageous to suppress or at least significantly reduce common mode noise on a differential signal route to achieve low electromagnetic emission (EME).